For lidocaine, a local anesthetic, various external preparations have previously been studied and the development of patches has progressed in recent years; several patches of lidocaine have been put on the market. To allow the anesthetic action to be exerted and improve pain in the deep part of the skin, approaches for enhancing the permeation of lidocaine into the skin are also studied; as one means therefor, patches containing lidocaine in higher concentrations are studied.
For example, Patent Document 1 discloses a tape preparation containing 20% by weight of lidocaine for the purpose of alleviating pain in centesis by an intravenous indwelling needle. Patent Document 2 discloses a preparation containing nearly 30% by weight of lidocaine. However, a high lidocaine content of about 20% by weight leads to the precipitation of a lidocaine crystal in a base of the preparation. The precipitation of the lidocaine crystal results in the dispersion of the undissolved drug in the adhesive mass; thus, in the application of the preparation to the skin or the like, a sufficient amount of the drug cannot be absorbed into the body, delaying the onset of the anesthetic effect. In addition, the problem arises that the drug remains on the skin or the like in peeling the tape preparation. The problem has also arisen that the precipitation of the drug crystal in the adhesive mass not only makes the appearance worse and but also reduces the adhesion.    Patent Document 1: Japanese Patent Laid-Open No. 2002-193795    Patent Document 2: Japanese Patent Laid-Open No. 07-215850